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I've installed LED lights in my car and I wanted to find a power source that will let it stay on for a while after turning off my car.

I noticed that the power windows still work after turning off my car until I open and close the door. So I tried tapping that fuse (42), but my lights stayed on even after closing the door.

The door power lock seemed to work similarly, but with a short time delay. It also kept providing power a couple minutes after turning off my car (fuse 15). Why do these still provide power when the features don't work? Are these two constant power sources?

(I just noticed there is a door lock fuse at 41. I will test that next)

For now, I've resorted to tapping the fuse for the accessory power, but the power cuts off as soon as I turn off my car. Is there any fuse I can tap that will provide power for a short while after turning off my car?

Honda Civic 2014 LX CVT Sedan Interior Fuse Box

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  • Have you considered a toggle switch for the LEDs?
    – Adam Miller
    Commented Apr 16, 2020 at 4:25

3 Answers 3

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On a modern car, the ECUs (electronic control units) will be deciding when different functions will work. For example, it knows to switch power to the window circuits until you open and close the door. The ECU could be controlling a relay that switches the power to the windows off when you shut the door. The fuse that you are connecting to will be before the relay in the circuit. Therefore if you wanted to tap into this power, you would have to connect your LEDs to the output of the relay.

Alternatively and more likely, there may not be a relay, and it may be that the ECU is watching the window buttons and deciding that it will only control the windows up until you have shut the door. This will be the same for the door locks, again the ECU will be making the decisions.

There won't be a fuse that keeps the power on for a period of time after switching the ignition off and adding additional load to the electronics on modern cars could cause all sorts of damage.

You could use one of these- http://www.ebay.com/itm/MP7505-Car-Ceiling-Light-Delay-Off-Timer-20-second-10W-12VDC-Electronic-Board-/140510927871

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  • Actually, in most modern vehicles it's the Body Control Module (BCM) which powers things like the radio and power windows after the vehicle is shut off ... this is a different piece of the pie than the ECU.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Nov 8, 2015 at 0:34
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    @Paulster2 ECU - Electronic Control Unit - en.m.wikipedia.org/wiki/Electronic_control_unit the BCM is an ECU. I wasn't referring to the ECM Engine Control Module
    – HandyHowie
    Commented Nov 8, 2015 at 9:32
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    Then please refer to it by its proper name ... when you use a generic term as such, people get confused. By your standards, you could apply ECU to the ABS or TCU for that matter. Neither of those have anything to do with what the BCM does. BCM makes more sense than the generic ECU. Someone really needs to delete that Wiki page.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Nov 8, 2015 at 10:51
  • @Paulster2. OK. Maybe it's the difference in our locations. The general public here would understand what an ECU was, but a BCM would then need explaining. Thanks.
    – HandyHowie
    Commented Nov 8, 2015 at 11:47
  • @HandyHowie Thanks for the explanation and part suggestion! I may end up getting the part if nothing else works, but I'll still be trying other ways just because I want to tinker and would prefer fewer dependencies.
    – Evie
    Commented Nov 9, 2015 at 23:58
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Try circuit #34 or #35. You don't necessarily have to do this in the vehicles fusebox. For instance; when I used to install a lot of Alpine audio/visual equipment, their ceiling-mounted LCD/DVD players had LEDs which required wiring up separately. So I would splice their power-feed directly into (out of) the original interior light's pre-existing wiring loom. I would typically include an inline fuse, solder the join, wrap it nice, and stash it in the hoodlining (ie. the ceiling upholstery). The LEDs would typically fade out with all the other interior lights, 30 seconds or so after removing the key from the ignition, and/or closing, and/or locking the doors.

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  • I'll give those fuses a try. Going by the information from @HandyHowie, I suspect the wires you spliced may have gone through the ECU? I'm tapping the fuses directly from the fuse box, so if that doesn't work, I may try splicing.
    – Evie
    Commented Nov 9, 2015 at 23:57
  • @KevinLau I'm fairly certain the interior lights wiring looms did not interface with the ECU directly, although I can't be 100% on that. It's possibly the case with more recent vehicles. I doubt it makes a difference though. As long as it provides ~12VDC+ at the appropriate times you should be fine. It's typically only the one wire to splice. I would recommend earthing directly to the chassis' bare metal.
    – voices
    Commented Nov 10, 2015 at 2:24
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We wired our LED's to interior light via switch on door as interior light stay's on for a while until car is locked.

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